Apparatuses, systems, and methods for determining location of a mobile device(s) in a distributed antenna system(s)

ABSTRACT

Distributed antenna systems provide location information for client devices communicating with remote antenna units. The location information can be used to determine the location of the client devices relative to the remote antenna unit(s) with which the client devices are communicating. A location processing unit (LPU) includes a control system configured to receive uplink radio frequency (RF) signals communicated by client devices and determines the signal strengths of the uplink RF signals. The control system also determines which antenna unit is receiving uplink RF signals from the device having the greatest signal strength.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/876,754, filed Jan. 22, 2018, which is a continuation of U.S. patentapplication Ser. No. 15/356,723, filed on Nov. 21, 2016, now U.S. Pat.No. 9,913,094, which is a continuation of U.S. patent application Ser.No. 14/873,483, filed Oct. 2, 2015, now U.S. Pat. No. 9,532,329, whichis continuation of U.S. patent application Ser. No. 14/034,948, filedSep. 24, 2013, now U.S. Pat. No. 9,185,674, which is a continuation ofU.S. patent application Ser. No. 13/365,843, filed on Feb. 3, 2012, nowU.S. Pat. No. 8,570,914, which is a continuation of International App.No. PCT/US2010/044884, filed on Aug. 9, 2010, the contents of which arerelied upon and incorporated herein by reference in their entireties,and the benefit of priority under 35 U.S.C. § 120 is hereby claimed.

BACKGROUND Field of the Disclosure

The technology of the disclosure relates to distributed antenna andcommunications systems, including mobile distributed telecommunicationsystems and networks, for distributing communications signals to remoteantenna units. The distributed antenna and communications systems caninclude any type of media, including but not limited to optical fiber toprovide an optical fiber-based distributed antenna system.

Technical Background

Wireless communication is rapidly growing, with ever-increasing demandsfor high-speed mobile data communication. As an example, so-called“wireless fidelity” or “WiFi” systems and wireless local area networks(WLANs) are being deployed in many different types of areas (e.g.,coffee shops, airports, libraries, etc.). Distributed antenna systemscommunicate with wireless devices called “clients” or “client devices,”which must reside within the wireless range or “cell coverage area” inorder to communicate with an access point device. A distributed antennasystem (DAS) comprises multiple antennas connected to a common cellularbase station and can provide cellular coverage over the same area as asingle antenna.

One approach to deploying a distributed antenna system involves the useof radio frequency (RF) antenna coverage areas, also referred to as“antenna coverage areas.” Antenna coverage areas can have a radius inthe range from a few meters up to twenty meters as examples. Combining anumber of access point devices creates an array of antenna coverageareas. Because the antenna coverage areas each cover a small area, thereare typically only a few users (clients) per antenna coverage area. Thisallows for minimizing the amount of RF bandwidth shared among thewireless system users.

A distributed antenna system can be implemented to provide adequatecellular telephone and internet coverage within an area where thepropagation of an RF signal is disturbed. For example, transmission andreception of RF signals are often blocked inside high buildings due tothick steel, concrete floors and walls. Similar problems can be found inother areas such as airports, shopping malls or tunnels, etc. Toovercome this coverage problem, a distributed antenna system maycomprise components that receive an input RF signal and convert it to awired signal, for example, an optical signal. The distributed antennasystem may include fiber optic cables to transmit optical signals in anarea where RF signals are blocked, e.g., inside the buildings. Theantennas can be placed close to the possible locations of mobile orportable terminals, originated from a utility or service room and thenarranged to form a star-like topology. The distributed antenna systemmay also comprise components that re-convert the wired signals back tothe RF signals.

As discussed above, it may be desired to provide such distributedantenna systems indoors, such as inside a building or other facility, toprovide indoor wireless communication for clients. Otherwise, wirelessreception may be poor or not possible for wireless communication clientslocated inside the building. In this regard, the remote antenna unitscan be distributed throughout locations inside a building to extendwireless communication coverage throughout the building. While extendingthe remote antenna units to locations in the building can provideseamless wireless coverage to wireless clients, other services may benegatively affected or not possible due to the indoor environment. Forexample, it may be desired or required to determine the location ofclient devices or provide localization services for client devices, suchas emergency 911 (E911) services as an example. If the client device islocated indoors, techniques such as global positioning services (GPSs)may not be possible to determine the location of the client device.Further, triangulation techniques may not be able to determine thelocation of the client device due to the remote antenna units typicallybeing arranged to avoid overlapping regions between antenna coverageareas.

SUMMARY OF THE DETAILED DESCRIPTION

Embodiments disclosed in the detailed description include distributedantenna apparatuses, systems, methods, and computer-readable mediums toprovide location information regarding client devices communicating withremote antenna units in a distributed antenna system. The locationinformation can be used to determine the location of the client devicesrelative to the remote antenna unit(s) in which the client devices arecommunicating. In this scenario, the client devices would be known to bewithin communication range of the remote antenna units. This informationcan be used to determine or provide a more precise area of location ofthe client devices. The distributed antenna components and systems, andrelated methods disclosed herein may be well suited for indoorenvironments where other methods of providing and/or determining thelocation of client devices may be obstructed or not possible due to theindoor environment.

In this regard, in certain embodiments disclosed herein, a locationprocessing unit (LPU) configured to provide location information for atleast one client device wirelessly communicating in a distributedantenna system can be provided. The LPU includes a control systemconfigured to receive uplink radio frequency (RF) signals communicatedby at least one client device wirelessly communicating to a plurality ofantenna units. The control system is further configured to determine thesignal strengths of the uplink RF signals. The control system is furtherconfigured to determine which antenna unit among the plurality ofantenna units is receiving uplink RF signals from the at least oneclient device having the greatest signal strength. The control system isfurther configured to determine location information for the at leastone client device based on identification of the antenna unit receivingthe uplink RF signals from the at least one client device having thegreatest signal strength.

In another embodiment, a method of determining location information forat least one client device wirelessly communicating in a distributedantenna system is provided. The method includes receiving uplink RFsignals communicated by at least one client device wirelesslycommunicating to a plurality of antenna units. The method furtherincludes determining the signal strengths of the uplink RF signals. Themethod further includes determining which antenna unit among theplurality of antenna units is receiving uplink RF signals from the atleast one client device having the greatest signal strength. The methodfurther includes determining the location of the at least one clientdevice based on identification of the antenna unit receiving the uplinkRF signals from the at least one client device having the greatestsignal strength.

In another embodiment, a computer-readable medium having stored thereoncomputer-executable instructions to cause an LPU configured to determinethe location of at least one client device wirelessly communicating in adistributed antenna system is provided. The computer-executableinstructions cause the LPU to receive uplink RF signals communicated byat least one client device wirelessly communicating to a plurality ofantenna units. The computer-executable instructions cause the LPU todetermine the signal strengths of the uplink RF signals. Thecomputer-executable instructions cause the LPU to determine whichantenna unit among the plurality of antenna units is receiving uplink RFsignals from the at least one client device having the greatest signalstrength. The computer-executable instructions cause the LPU todetermine location information for the at least one client device basedon identification of the antenna unit receiving the uplink RF signalsfrom the at least one client device having the greatest signal strength.

In another embodiment, a head-end unit configured to determine thelocation of at least one client device wirelessly communicating in adistributed antenna system is provided. The head-end unit comprises anuplink receiver (URX) configured to receive uplink RF signalscommunicated by at least one client device wirelessly communicating to aplurality of antenna units. The URX is further configured to determinethe signal strengths of the uplink RF signals. The URX is furtherconfigured to provide the signal strengths of the uplink RF signals toan LPU. The LPU is configured to determine which antenna unit among theplurality of antenna units is receiving uplink RF signals from the atleast one client device having the greatest signal strength. The LPU isfurther configured to determine location information for the at leastone client device based on identification of the antenna unit receivingthe uplink RF signals from the at least one client device having thegreatest signal strength.

Embodiments disclosed herein also include apparatuses and methods fordetermining the location of a mobile terminal in a distributed antennasystem (DAS). An additional LPU is coupled to a typical DAS andpreferably integrated in the head-end unit. Each RF uplink signal istransmitted to the LPU before being combined together and all of thesplit downlink signals are sent to the LPU as well. The LPU iscommunicatively linked to the base station and sends the locationinformation of all distributed antennas to the base station. In order toextract the location information of a mobile terminal, the LPU monitorsthe usage of the frequency band which follows the long term evolution(LTE) standard.

In accordance with another embodiment, apparatuses for determining thelocation of a mobile terminal are provided and comprise a distributedantenna system that includes multiple antennas located in an indoorregion where each of the antennas is located in a known area andprovides a respective coverage area for communicating with a mobileterminal; a head-end unit that distributes the downlink signals andcombines the uplink signals; and an LPU that is integrated in thehead-end unit and is communicatively linked to the base station. The RFtransmission signals in the system are modulated according to the LTEstandard.

In accordance with another embodiment, apparatuses for determining thelocation of a mobile terminal, the location processing unit (LPU), areprovided and comprise a plurality of signal monitoring devices thatreceive each of the uplink signals transmitted by the multiple antennaslocated in the known areas and acquire the time slots of the downlinksignals sent by the base station and split by the head-end unit; and alocation server that identifies a transmitting mobile terminal bymonitoring the usage of the frequency band and sends the locationinformation to the base station.

In accordance with another embodiment, methods for determining thelocation of a mobile terminal are provided and comprise selecting aspecific time slot from the downlink signals; calculating the receivedsignal strength indication (RSSI) values for each of the resource blocksat the specific time slot from the uplink signals; delivering the RSSIvalues of all the antennas to the location server of the LPU; andidentifying which of the antennas is closest to the transmitting mobileterminal by monitoring RSSI values.

In accordance with one feature in the method for determining thelocation of a mobile terminal, the signal processing steps includeconverting the RF signals acquired from both downlink and uplink tobaseband by transceivers (TRXs); digitizing the downlink and uplinksignals by a pair of analog-to-digital converters (ADCs); selecting thespecific window of data samples from the sample streams by timesynchronization; and calculating the RSSI values for each of theresource blocks by a fast Fourier transform (FFT).

In according with a modification of embodiments disclosed herein, thelocation information comprising of the maximum RSSI values with therespective antenna locations where those maximum values have beenreceived are provided to the base station, which then combines thislocation information with the prior user allocation to provide alocation estimate to the network.

In a further modification of the method, the downlink and the uplink RFsignals are temporal synchronized by means of standard techniques usedin mobile terminal devices.

In another embodiment, the RSSI values for each of the resource blocks(RB) are calculated by an FFT.

In another modification, the location information of the transmittingmobile terminal is sent to the base station. An alternative embodimentof the method is to instruct the mobile device to modulate its outputpower, to identify a received signal from the mobile device havingmodulated output power; and to identify a particular antenna unit havinga highest received power level from the mobile device.

Another embodiment of the method is provided by using time divisionmultiple access (TDMA) protocol to identify a received signal from themobile device in a frequency channel and time slot of the mobile device;and to determine which of the antennas is closest to the mobile deviceto be located by monitoring received signal strength of the identifiedsignal.

Additional features and advantages will be set forth in the detaileddescription which follows, and in part will be readily apparent to thoseskilled in the art from that description or recognized by practicing theembodiments as described herein, including the detailed description thatfollows, the claims, as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description present embodiments, and are intendedto provide an overview or framework for understanding the nature andcharacter of the disclosure. The accompanying drawings are included toprovide a further understanding, and are incorporated into andconstitute a part of this specification. The drawings illustrate variousembodiments, and together with the description serve to explain theprinciples and operation of the concepts disclosed.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic diagram of an exemplary distributed antennasystem;

FIG. 2 is a partially schematic cut-away diagram of an exemplarybuilding infrastructure in which a distributed antenna system can beemployed;

FIG. 3 is an exemplary schematic diagram of an exemplary head-end unit(HEU) deployed in an distributed antenna system;

FIG. 4 shows an example of resource allocation in the frequency-timegrid, received from a particular remote antenna unit(s) (RAUs) in adistributed antenna system;

FIG. 5 is a schematic diagram of an exemplary distributed antenna systemillustrating location of client devices in relation to theircommunication with one or more RAUs in the distributed antenna system;

FIG. 6 is a schematic diagram of a distributed antenna system integratedwith a location processing unit (LPU) in accordance with one embodiment;

FIG. 7 is a schematic diagram illustrating more detail of the internalcomponents of an exemplary LPU, which may include the LPU of FIG. 6;

FIG. 8 is a schematic diagram illustrating exemplary signal processingsteps that can be performed by an LPU, including the LPU in FIGS. 6 and7, to provide location processing and location services;

FIG. 9A is a schematic diagram of the HEU in FIG. 3 that includes an LPUand other components to determine location of client devices in adistributed antenna system;

FIG. 9B is a schematic diagram of an alternative HEU that includes aco-located LPU and downlink receiver (DRX);

FIG. 10 is a schematic diagram illustrating components that may beincluded in an LPU, including the LPU in FIGS. 6, 9A, and 9B;

FIG. 11 is a schematic diagram of an exemplary downlink base stationinterface card (BIC) that can be provided in the exemplary HEU in FIG.9A;

FIG. 12 is a schematic diagram of an exemplary DRX that can be providedin the exemplary HEU in FIGS. 9A and 9B;

FIG. 13 is a schematic diagram of an exemplary uplink BIC that can beprovided in the exemplary HEU in FIGS. 9A and 9B;

FIG. 14 is a schematic diagram of an exemplary uplink receiver (URX)that can be provided in the exemplary HEU in FIGS. 9A and 9B;

FIG. 15 is a schematic diagram of an exemplary uplink spectrum analyzerprovided in the URX in FIG. 14;

FIG. 16 is an exemplary URX message communicated from a URX to an LPU toprovide energy levels associated with RAUs assigned to the URX forclient device communications to the RAUs;

FIG. 17 is an exemplary LPU message communicated from an LPU to a basestation to provide RAUs associated with the maximum energy level forclient device communications;

FIG. 18 is a schematic diagram of an exemplary HEU board configuration;

FIG. 19 is a schematic diagram of another exemplary HEU boardconfiguration;

FIG. 20 is a schematic diagram of a master HEU configured to providelocation information for client devices communicating with a pluralityof slave HEUs communicatively coupled to the master HEU;

FIG. 21 is a graph illustrating exemplary time-frequency separation ofclient devices;

FIG. 22 is a graph illustrating exemplary SC-FDMA spectrum of a 0 dBSC-FDMA signal compared to noise level;

FIG. 23 is a graph illustrating exemplary false detection probabilityfor one client device and one resource block (RB);

FIG. 24 is a graph illustrating exemplary probability of not having 10RBs pointing to the same RAU;

FIG. 25 is a graph illustrating exemplary probability of not having 100RBs pointing to the same RAU;

FIG. 26 is a graph illustrating exemplary energy leakage caused byfrequency offset;

and

FIG. 27 is a graph illustrating exemplary energy leakage caused by timeoffset.

DETAILED DESCRIPTION

Reference will now be made in detail to the embodiments, examples ofwhich are illustrated in the accompanying drawings, in which some, butnot all embodiments are shown. Indeed, the concepts may be embodied inmany different forms and should not be construed as limiting herein;rather, these embodiments are provided so that this disclosure willsatisfy applicable legal requirements. Whenever possible, like referencenumbers will be used to refer to like components or parts.

Embodiments disclosed in the detailed description include distributedantenna apparatuses, systems, methods, and computer-readable mediums toprovide location information regarding client devices communicating withremote antenna units in a distributed antenna system. Providing locationinformation is also providing “location services.” The locationinformation can be used to determine the location of the client devicesrelative to the remote antenna unit(s) in which the client devices arecommunicating. In this scenario, the client devices would be known to bewithin communication range of the remote antenna units. This informationcan be used to determine or provide a more precise area of location ofthe client devices. The distributed antenna components and systems, andrelated methods disclosed herein may be well suited for indoorenvironments where other methods of providing and/or determining thelocation of client devices may be obstructed or not possible due to theindoor environment.

In this regard, in certain embodiments disclosed herein, a locationprocessing unit (LPU) configured to provide location information for atleast one client device wirelessly communicating in a distributedantenna system can be provided. The LPU includes a control systemconfigured to receive uplink radio frequency (RF) signals communicatedby at least one client device wirelessly communicating to a plurality ofantenna units. The control system is further configured to determine thesignal strengths of the uplink RF signals. The control system is furtherconfigured to determine which antenna unit among the plurality ofantenna units is receiving uplink RF signals from the at least oneclient device having the greatest signal strength. The control system isfurther configured to determine location information for the at leastone client device based on identification of the antenna unit receivingthe uplink RF signals from the at least one client device having thegreatest signal strength.

Before discussing the exemplary apparatuses, systems, methods, andcomputer-readable mediums that are configured to determine locationinformation of a client device(s) in a distributed antenna systemstarting at FIG. 5, exemplary distributed antenna systems that do notinclude location processing according to embodiments disclosed hereinare first described with regard to FIGS. 1-4.

Distributed antenna systems can employ different transmission mediums,including for example, conductive wire and optical fiber. A possibleconfiguration of a distributed antenna system using fiber optic cablesis shown in FIG. 1. In this regard, FIG. 1 is a schematic diagram of ageneralized embodiment of an antenna system. In this embodiment, theantenna system is a distributed antenna system 10. The distributedantenna system 10 is configured to create one or more antenna coverageareas for establishing communications with wireless client deviceslocated in the radio frequency (RF) range of the antenna coverage areas.In this regard, the distributed antenna system 10 includes a head-endunit (HEU) 12, one or more remote antenna units (RAUs) 14 and an opticalfiber link 16 that optically couples the HEU 12 to the RAU 14. The HEU12 is configured to receive communications over downlink electrical RFsignals 18D from a source or sources, such as a network or carrier asexamples, and provide such communications to the RAU 14. The HEU 12 isalso configured to return communications received from the RAU 14, viauplink electrical RF signals 18U, back to the source or sources. In thisregard, in this embodiment, the optical fiber link 16 includes at leastone downlink optical fiber 16D to carry signals communicated from theHEU 12 to the RAU 14 and at least one uplink optical fiber 16U to carrysignals communicated from the RAU 14 back to the HEU 12.

The distributed antenna system 10 has an antenna coverage area 20 thatcan be substantially centered about the RAU 14. The antenna coveragearea 20 of the RAU 14 forms an RF coverage area 21. The distributedantenna system 10 in this example is an optical fiber-based distributedantenna system. In this regard, the HEU 12 is adapted to perform or tofacilitate any one of a number of Radio-over-Fiber (RoF) applications,such as radio-frequency (RF) identification (RFID), wireless local-areanetwork (WLAN) communication, or cellular phone service.“Radio-over-Fiber,” or “RoF,” utilizes RF signals sent over opticalfibers. Shown within the antenna coverage area 20 is a client device 24in the form of a mobile device as an example, which may be a cellulartelephone as an example. The client device 24 can be any device that iscapable of receiving RF communication signals. The client device 24includes an antenna 26 (e.g., a wireless card) adapted to receive and/orsend electromagnetic RF signals.

As discussed above, the distributed antenna system 10 may, but is notrequired to, employ RoF. RoF is a technology whereby light is modulatedby a radio signal and transmitted over an optical fiber link tofacilitate wireless access. In an RoF architecture, a data-carrying RFsignal with a high frequency (e.g. only, greater than 10 GHz) is imposedon a lightwave signal before being transported over the optical link.Therefore, wireless signals are optically distributed to base stationsdirectly at high frequencies and converted to from optical to electricaldomain at the base stations before being amplified and radiated by anantenna. As a result, no frequency up/down conversion is required at thevarious base station, thereby resulting in simple and rathercost-effective implementation is enabled at the base stations.

With continuing reference to FIG. 1, to communicate the electrical RFsignals over the downlink optical fiber 16D to the RAU 14, to in turn becommunicated to the client device 24 in the antenna coverage area 20formed by the RAU 14, the HEU 12 includes an electrical-to-optical (E/O)converter 28. The E/O converter 28 converts the downlink electrical RFsignals 18D to downlink optical RF signals 22D to be communicated overthe downlink optical fiber 16D. The RAU 14 includes anoptical-to-electrical (O/E) converter 30 to convert received downlinkoptical RF signals 22D back to electrical RF signals to be communicatedwirelessly through an antenna 32 of the RAU 14 to client devices 24located in the antenna coverage area 20. The antenna 32 may be referredto as a “remote antenna unit 32” herein, but such only means that theantenna 32 is located a desired distance from the HEU 12.

Similarly, the antenna 32 is also configured to receive wireless RFcommunications from client devices 24 in the antenna coverage area 20.In this regard, the antenna 32 receives wireless RF communications fromclient devices 24 and communicates electrical RF signals representingthe wireless RF communications to an E/O converter 34 in the RAU 14. TheE/O converter 34 converts the electrical RF signals into uplink opticalRF signals 22U to be communicated over the uplink optical fiber 16U. AnO/E converter 36 provided in the HEU 12 converts the uplink optical RFsignals 22U into uplink electrical RF signals, which can then becommunicated as uplink electrical RF signals 18U back to a network orother source. The HEU 12 in this embodiment is not able to distinguishthe location of the client devices 24 in this embodiment. The clientdevice 24 could be in the range of any antenna coverage area 20 formedby an RAU 14.

To provide further exemplary illustration of how a distributed antennasystem, such as distributed antenna system 10 in FIG. 1, can be deployedindoors, FIG. 2 is a partially schematic cut-away diagram of a buildinginfrastructure 40 employing the distributed antenna system 10 of FIG. 2.The building infrastructure 40 generally represents any type of buildingin which the distributed antenna system 10 can be deployed. Aspreviously discussed with regard to FIG. 1, the distributed antennasystem 10 incorporates the HEU 12 to provide various types ofcommunication services to coverage areas within the buildinginfrastructure 40, as an example. For example, as discussed in moredetail below, the distributed antenna system 10 in this embodiment isconfigured to receive wireless RF signals and convert the RF signalsinto RoF signals to be communicated over the optical fiber link 16 tothe RAUs 14. The distributed antenna system 10 in this embodiment canbe, for example, an indoor distributed antenna system (IDAS) to providewireless service inside the building infrastructure 40. These wirelesssignals can include cellular service, wireless services such as radiofrequency identification (RFID) tracking, Wireless Fidelity (WiFi),local area network (LAN), and combinations thereof, as examples.

With continuing reference to FIG. 2, the building infrastructure 40includes a first (ground) floor 42, a second floor 44, and a third floor46. The floors 42, 44, 46 are serviced by the HEU 12 through a maindistribution frame 48 to provide antenna coverage areas 50 in thebuilding infrastructure 40. Only the ceilings of the floors 42, 44, 46are shown in FIG. 2 for simplicity of illustration. In the exampleembodiment, a main cable 52 has a number of different sections thatfacilitate the placement of a large number of RAUs 14 in the buildinginfrastructure 40. Each RAU 14 in turn services its own coverage area inthe antenna coverage areas 50. The main cable 52 can include, forexample, a riser section 54 that carries all of the downlink and uplinkoptical fibers 16D, 16U to and from the HEU 12. The main cable 52 caninclude one or more multi-cable (MC) connectors adapted to connectselect downlink and uplink optical fibers 16D, 16U, along with anelectrical power line, to a number of optical fiber cables 56.

The main cable 52 enables multiple optical fiber cables 56 to bedistributed throughout the building infrastructure 40 (e.g., fixed tothe ceilings or other support surfaces of each floor 42, 44, 46) toprovide the antenna coverage areas 50 for the first, second and thirdfloors 42, 44 and 46. In an example embodiment, the HEU 12 is locatedwithin the building infrastructure 40 (e.g., in a closet or controlroom), while in another example embodiment the HEU 12 may be locatedoutside of the building infrastructure 40 at a remote location. A basestation 58, which may be provided by a second party such as a cellularservice provider, is connected to the HEU 12, and can be co-located orlocated remotely from the HEU 12. A base station is any station orsource that provides an input signal to the HEU 12 and can receive areturn signal from the HEU 12. In a typical cellular system, forexample, a plurality of base stations are deployed at a plurality ofremote locations to provide wireless telephone coverage. Each basestation serves a corresponding cell and when a mobile station enters thecell, the base station communicates with the mobile station. Each basestation can include at least one radio transceiver for enablingcommunication with one or more subscriber units operating within theassociated cell.

To provide further detail on components that can be provided in a HEU,including the HEU 12 provided in the distributed antenna system 10 ofFIGS. 1 and 2, FIG. 3 is provided. As illustrated therein, the HEU 12 inthis embodiment includes a head-end controller (HEC) 60 that manages thefunctions of the HEU 12 components and communicates with externaldevices via interfaces, such as a RS-232 port 62, a Universal Serial Bus(USB) port 64, and an Ethernet port 66, as examples. The HEU 12 can beconnected to a plurality of base stations (BTSs) 69(1)-69(N),transceivers, and the like via base station inputs 70 and base stationoutputs 72. The base station inputs 70 are downlink connections and thebase station outputs 72 are uplink connections. Each base station input70 is connected to a downlink base station interface card (BIC) 74located in the HEU 12, and each base station output 72 is connected toan uplink BIC 76 also located in the HEU 12. The downlink BIC 74 isconfigured to receive incoming or downlink RF signals from the basestation inputs 70 and split the downlink RF signals into copies to becommunicated to the RAUs 14, as illustrated in FIG. 4. The uplink BIC 76is configured to receive the combined outgoing or uplink RF signals fromthe RAUs 14 and split the uplink RF signals into individual base stationoutputs 72 as a return communication path.

The downlink BIC 74 is connected to a midplane interface card 78 panelin this embodiment. The uplink BIC 76 is also connected to the midplaneinterface card 78. The downlink BIC 74 and uplink BIC 76 can be providedin printed circuit boards (PCBs) that include connectors that can plugdirectly into the midplane interface card 78. The midplane interfacecard 78 is in electrical communication with a plurality of opticalinterface cards (OICs) 80, which provide an optical to electricalcommunication interface and vice versa between the RAUs 14 via thedownlink and uplink optical fibers 16D, 16U and the downlink BIC 74 anduplink BIC 76. The OICs 80 include the E/O converter 28 in FIG. 2 thatconverts electrical RF signals from the downlink BIC 74 to optical RFsignals, which are then communicated over the downlink optical fibers16D to the RAUs 14 and then to client devices. The OICs 80 also includethe O/E converter 36 in FIG. 1 that converts optical RF signalscommunicated from the RAUs 14 over the uplink optical fibers 16U to theHEU 12 and then to the base station outputs 72.

The OICs 80 in this embodiment support up to three (3) RAUs 14 each. TheOICs 80 can also be provided in a PCB that includes a connector that canplug directly into the midplane interface card 78 to couple the links inthe OICs 80 to the midplane interface card 78. The OICs 80 may consistof one or multiple optical interface cards (OICs). In this manner, theHEU 12 is scalable to support up to thirty-six (36) RAUs 14 in thisembodiment since the HEU 12 can support up to twelve (12) OICs 80. Ifless than thirty-six (36) RAUs 14 are to be supported by the HEU 12,less than twelve OICs 80 can be included in the HEU 12 and plugged intothe midplane interface card 78. One OIC 80 is provided for every three(3) RAUs 14 supported by the HEU 12 in this embodiment. OICs 80 can alsobe added to the HEU 12 and connected to the midplane interface card 78if additional RAUs 14 are desired to be supported beyond an initialconfiguration. The HEC 60 can also be provided that is configured to beable to communicate with the downlink BIC 74, the uplink BIC 76, and theOICs 80 to provide various functions, including configurations ofamplifiers and attenuators provided therein. Note that although FIG. 3illustrates specific exemplary components for the HEU 12, the HEU 12 isnot limited to such components.

It may be desired to provide location information/localization servicesin the distributed antenna system 10 illustrated in FIGS. 1 and 2, as anexample. For example, it may be desired determine the location of clientdevices 24 communicating with antennas 32 in the distributed antennasystem 10. Localization services may be desired or required to providecertain services, such as, for example, emergency 911 (E911) services inthe case of a cellular client device. Localization services may requirea certain percentage of client devices 24 to be locatable within a givendistance to comply with communication requirements. As an example, itmay be desired or required by E911 services to be able to locate a givenpercentage of all client device users within one hundred (100) feet(ft.) as an example. Localization services may be desired or requiredfor other types of wireless clients other than cellular clients as well.If client devices 24 are located inside the building infrastructure 40and establishe communication with the HEU 12, it can be determined thatthe client devices 24 are located within at least the distance betweenthe farthest RAU 14 located from the HEU 12. However, it may not bepossible to determine the location of client devices 24 with greaterspecificity and resolution. For example, in indoor environments, globalpositioning services (GPSs) provided in the client devices 24 may beinoperable to report a location. Further, triangulation techniques as amethod of determining location of client devices 24 may not be possibledue to separation of the antenna coverage areas in the distributedantenna system 10.

If it could be determined to which RAU(s) 14 in the distributed antennasystem 10 a client device 24 establishes communications, thisinformation could be used to provide location information for a clientdevice 24. The client device 24 would be known to be withincommunication range of such RAU(s) 14. This information coupled withknowing the location of the HEU 12 can be used to determine or provide amore precise area of location of the client device 24. In essence,linking communication of client devices 24 with a particular RAU(s) 14provides another layer of location determination in addition to knowingthe location of the HEU 12. Cellular networks, for example, providemethods of determining location.

For example, Global System for Mobile Communications (GSM) networkcompatible client devices are configured to automatically initiateproviding client device identification information over the network thatcan be exploited to provide location services for a distributed antennasystem. The locations of the RAUs in the system are also configured andknown in the HEU. By knowing and correlating the particular RAU(s) inwhich the client device established communication, the HEU is able todetermine and/or provide the location of the client device as beingwithin the antenna coverage area formed by the particular RAU. Thecorrelation of client device identification information from the clientdevice with the location of the RAU is retained when communicated to theHEU and is not lost by being combined, such as by splitters orcontainers, with communications from other RAUs.

As another example, in a code division multiple access (CDMA) network, aspecific notification channel is provided to carry a tracking signalthat can be exploited to provide location services in a distributedantenna system. In this manner, the tracking signal is radiated throughthe RAU to be communicated to client devices within range of the antennacoverage area formed by the RAU. When the client device wirelesslyreceives the tracking signal, the client device communicates itsidentification information and identification of the tracking signal toan RAU to be communicated back to the HEU. The HEU can provide thisinformation to a network or carrier. In this manner, the client deviceidentification information and identification of the tracking signal canbe associated with the location of a particular RAU(s) that received andtransmitted the tracking signal in the distributed antenna system toprovide or determine a location of the client device.

As another example, the long term evolution (LTE) standard supports bothfrequency division duplexing (FDD) and time division duplexing (TDD)modes that can be exploited to provide location services in adistributed antenna system. LTE uses orthogonal frequency-divisionmultiplexing (OFDM) for the downlink and a pre-coded version of OFDMcalled single carrier-frequency division multiple access (SC-FDMA) forthe uplink. Furthermore, LTE employs a multiple input/multiple output(MIMO) antenna scheme to achieve the requirements of throughput andspectral efficiency. The LTE standard supports both FDD and TDD modes.In the time domain, the time slot is fixed to 0.5 milliseconds (ms) longwhich is half of a subframe. A radio frame is ten (10) ms long and itcontains ten (10) subframes. In the frequency domain, the smallestresource unit is denoted as a resource element and twelve of theseelements together (per slot) are called a resource block (RB) that is180 kiloHertz (kHz). Uplink and downlink transmissions are separated inthe frequency domain. For TDD mode, a subframe is either allocated todownlink or uplink transmission. Uplink and downlink transmissionsalternate in the time domain using the same frequency bands.

In this regard, FIG. 4 illustrates that in an uplink, data is allocatedin multiples of one resource block. In FDD applications, the uplinkresource block size in the frequency domain contains twelve (12)sub-carriers and the transmission time interval is one (1) ms long. Theuplink resource blocks are assigned to the user equipment (UE) by thebase station scheduler, which is called evolved Node B (eNB). Since thebase station assigns certain time (t) and frequency (f) blocks to theUEs and informs UEs about the transmission format to use, the basestation has complete knowledge of which user has used a specificfrequency bin at a specific time slot. The UEs may hop resource blocksRB from subframe to subframe. In LTE PUSCH hopping mode, a UE may evenuse different frequencies from one slot to another for added frequencydiversity. FIG. 4 shows an exemplary diagram of resource allocation inthe frequency-time grid, received from a particular antenna in thedistributed antenna system. As shown in FIG. 4, the UE hops to anotherfrequency allocation from one slot to another within one subframe.

Since there is a growing demand for increasing the capacity and speed ofmobile telecommunication networks, mobile communication technology iscurrently being developed toward the 4th generation (4G), which ismainly based on the LTE standard. Therefore, it is desired to provide amethod for determining the location of a mobile terminal in adistributed antenna system that can meet the LTE standard.

In each of these technologies and any others that may be selected foremployment in a distributed antenna system, if communications betweenclient devices and particular RAU(s) can be determined and recognized,the location of the client devices in the distributed antenna system canbe determined. Depending on the communication technologies employed orsupported in a distributed antenna system, how a particular RAU islinked to a particular client device can vary, but the concept oflinking particular RAU(s) to client devices to determine location can beemployed.

In this regard, FIG. 5 illustrates a schematic diagram of an exemplarydistributed antenna system 90 that is configured to provide localizationservices for locating particular client devices 92 communicating withRAUs 94A-94D within the distributed antenna system 90. In this example,the RAUs 94A-94D are strategically located within different trackingzones 96A-96D in a building 98 or other infrastructure. For example,FIG. 5 illustrates four tracking zones 96A-96D, which may each representa given floor within the building 98. Note that although four (4)tracking zones 96A-96D are shown, the disclosure herein is not limitedto providing a particular number of tracking zones. Thus, when theclient devices 92 are located within range of a particular RAU 94A-94D,the client device 92 will communicate with a particular RAU(s) 94A-94Din range.

With continuing reference to FIG. 5, an HEU 102 provided in thedistributed antenna system 90 and communicatively coupled to the RAUs94A-94D can receive communications from the client devices 92 anddetermine from which RAU(s) 94A-94D communications from the clientdevices 92 are being received. Thus, location information regarding theclient devices 92 can be determined based on linking communications ofthe client devices 92 to known locations of the RAUs 94A-94D in thedistributed antenna system 90. The location information can be providedby the HEU 102 over a wired and/or wireless network 104 to a basestation 106, if desired. The base station 106 may contain informationthat allows the client devices 92 to be specifically identified by useror subscriber to then know the location of such user or subscriber.

Embodiments disclosed herein include modified HEUs that provideexemplary solutions to locate client devices based on theircommunications with a particular RAU(s) in a distributed antenna system.In this regard, FIG. 6 provides one embodiment of determining thelocation of a client device in a distributed antenna system. Asillustrated therein, a distributed antenna system 110 is provided, whichin this example is an optical fiber-based distributed antenna system.The distributed antenna system 110 contains multiple antennas 32provided in remote antenna units (RAU) 14 that provide respectivecoverage areas for communicating with client devices 24, which may befor example cellular devices and/or terminals. A main antenna 32 and anauxiliary antenna 32′ may be provided for antenna diversity. A HEU 116is provided that is communicatively coupled to a base station 118, whichmay be a cellular base station, to receive input electrical RF signals120 from the base station 118 and provide output electrical RF signals122 to the base station 118.

The HEU 116 includes a combiner/splitter 124 that splits the inputelectrical RF signals 120 into downlink electrical RF signals 126. Aplurality of RF-to-FO (RF2FO) converters 130 are provided to convert thedownlink electrical RF signals 126 to downlink optical RF signals 132.The downlink optical RF signals 132 are transmitted in an indoor regionvia fiber optic cables 134 and converted back to downlink electrical RFsignals 136 by a plurality of FO-to-RF (FO2RF) converters 138. Theconverted downlink electrical RF signals 136 are further transmitted tothe multiple antennas 32 for communicating with the client devices 24. Aplurality of RF2FO converters 140 are also provided to convert uplinkelectrical RF signals 142 from the client devices 24 to uplink opticalRF signals 144. The uplink optical RF signals 144 are communicated overfiber optic cables 146 to FO2RF converters 148 at the HEU 116 to beconverted into uplink electrical RF signals 128. The combiner/splitter124 combines the uplink electrical RF signals 128 into the outputelectrical RF signals 122 communicated to the base station 118.

If the client device 24 sends an RF signal to any of the antennas 32 inthis embodiment, the base station 118 cannot identify the location ofthe client device 24. This is because the uplink electrical RF signals128 from the various client devices 24 are combined by thecombiner/splitter 124. Thus, in this embodiment, a location processingunit (LPU) 150 is provided and integrated into the HEU 116. As will bedescribed in more detail below, the LPU 150 can determine the locationof the client devices 24. In certain embodiments, the LPU 150 candetermine the location of the client devices 24 by monitoring the signalstrength of the uplink electrical RF signals 142 received from theclient devices 24. By monitoring the signal strength of the uplinkelectrical RF signals 142 (either by direct measurement or indirectlysuch as measuring the signal strength of the uplink optical RF signals144) the LPU 150 can determine with which antenna 32 in the distributedantenna system 110 the client device 24 is communicating. If the clientdevice 24 is communicating with multiple antennas 32, the LPU 150 candistinguish which antenna 32 is closest to the client device 24 bycomparing the signal strengths of the uplink electrical RF signals 142received by the multiple antennas 32. The LPU 150 can then provide thislocation information regarding the client device 24 to the base station118 via a communication link 152, which may be a wired or wireless link.

FIG. 7 is a schematic diagram of one possible embodiment of the LPU 150in FIG. 6. In this regard, a plurality of signal monitoring devices154(1)-154(N) receive the uplink electrical RF signals 128(1)-128(N)from each of the distributed antennas 32 located in the known areasbefore being combined together by the HEU 116 and acquire the time slotsof the downlink electrical RF signals 126 sent by the base station 118after being split by the HEU 116. The task of the signal monitoringdevices 154(1)-154(N) is to provide the usage of the frequency band fromeach of the multiple antennas 32 (see FIG. 6). For each of the uplinkelectrical RF signals 128(1)-128(N), the received signal strengthindication (RSSI) value is determined by the signal monitoring devices154(1)-154(N) for given time/frequency blocks. A location server 156receives RSSI values of all of the antennas sent by the signalmonitoring devices 154(1)-154(N) and identifies which of the antennas 32is closest to the transmitting client device 24 to be located. Thelocation information is then sent over the communication link 152 to thebase station 118. Since the base station 118 controls the assignment ofcertain time slot/frequency blocks to the client devices 24 in thisembodiment, the base station 118 can uniquely identify which of theclient devices 24 has used a specific frequency bin at a specific timeslot.

In case of an emergency or a service request sent by the client device24, the base station 118 is asked to deliver the location informationand it sends the request to the LPU 150. Then, the LPU 150 acquires RSSIvalues for all particular time slots/frequency blocks from all theantennas and identifies the location of the transmitting client device24 by identifying the antenna 32 for which the resource block (RB)energy is maximized. The location information is then sent from the LPU150 to the base station 118 over the communication link 152. Anassessment of these RSSI values (e.g., triangulation) provides a goodestimation of the location in which the client device 24 is sending theservice request by monitoring the usage of the frequency band, and it iscommunicatively linked to the base station 118.

FIG. 8 is a schematic diagram illustrating exemplary signal processingsteps that can be performed by an LPU, including the LPU 150 in FIGS. 6and 7, to provide location processing and location services for locatingclient devices. The signal processing is performed in the LPU 150 forantenna diversity, for example, when two receiving antennas 32, 32′ perantenna location are employed for communications to the client device24. The downlink electrical RF signal 126 is first down-converted tobaseband by means of a transceiver (TRX) 158 that includes at leastmixers and appropriate filters. The downlink electrical RF signal 126 isthen digitized by a pair of analog-to-digital converters (ADCs) 160 toproduce downlink data 162.

With continuing reference to FIG. 8, the uplink electrical RF signal 128received from the main antenna 32 at a specific location is converted todigital baseband by a TRX 164 and ADCs 166 to produce uplink data 168.Time synchronization 170 of the downlink data 162 and the uplink data168 is processed by means of standard techniques that are also employedin client devices 24. For a given time slot (as illustrated in FIG. 4),the signal from the time synchronization 170 is used in a windowselection 172 to select a specific window of data samples from thesample streams to process a fast Fourier transform (FFT) 174. Thesquared absolute value of each FFT output is computed in step 176 andthe relevant outputs are combined to form an RSSI value for the giventime slot/frequency block in step 178.

Optionally, a second received uplink electrical RF signal 128′ comingfrom an auxiliary antenna 32′ at the same antenna location can beprocessed in the same manner. Uplink data 180 of this second pathconsisting of a TRX 182 and ADCs 183 are then combined together with theRSSI outputs of the main receiving antenna 32 in step 178 and thiscombined RSSI value can provide a better location estimation.

In an alternative embodiment applicable to TDD mode, in which uplink anddownlink transmissions alternate in the time domain using the samefrequency bands, a switching mechanism can be used to alternate thedownlink and uplink transmissions on the same frequency. However, thedownlink time synchronization block must additionally assess the controlinformation about the downlink and uplink periods. In LTE, this controlinformation can be retrieved from one of the control channels from thedownlink. An additional signal needs to be generated and conveyed to theuplink signal processing paths to exclude downlink signals from beingprocessed. Alternatively, a signal provided by the base station that isused to control a power amplifier in a TDD system can be used instead.

Now that generalized embodiments of providing location services havebeen described, more specific exemplary embodiments are discussed. Inthis regard, FIG. 9A is a schematic diagram of the HEU 12 in FIG. 3 thatincludes another example of an LPU and other components to determinelocation of client devices in a distributed antenna system. Componentsin FIG. 7 that are common with components in FIG. 3 are illustrated withcommon element numbers and thus will not be re-described here. Toprovide location information, an LPU 184 is provided in the HEU 12 andis interfaced with other additional components provided in the HEU 12.In FIG. 9A, the LPU 184 is provided as a separately component from adigital receiver (DRX) 186, which is discussed in more detail below.Alternatively, as illustrated in FIG. 9B, the LPU 184 and DRX 186 may beco-located in the same component, for example on the same PCB. The LPU184 is the main interface to the base stations 69(1)-69(N) viacommunication links 192. The base stations 69(1)-69(N) can requestlocation processing services over the communication links 192 to the LPU184. In response, the LPU 184 can configure a downlink receiver (DRX)186 and uplink receivers (URXs) 190, which are described in more detailbelow. The URXs 190 provide a distributed configuration to provideinformation regarding energy levels of the uplink optical RF signals 22Uresulting from client device 24 communications to antennas at RAUs 14coupled to the HEU 12 to the LPU 184. The LPU 184 uses the energy levelsto determine which antenna 32 (i.e., RAU) is closest to the clientdevice 24 to perform location services. More detail regarding internalexemplary components of the LPU 184 is provided in FIG. 10 describedbelow.

With continuing reference to FIG. 9A, the DRX 186 is provided toretrieve specific settings from a downlink control channel sent by abase station 69(1)-69(N) over downlink electrical RF signals188(1)-188(N) from the base station 69(1)-69(N). These settings are sentto the LPU 184 for analysis and control generation for analyzerfunctions performed by the LPU 184 for determining location of theclient devices 24. The DRX 186 uses the downlink electrical RF signals188(1)-188(N) to synchronize a local oscillator. The DRX 186 alsoprovides a reference frequency and reference timing to the LPU 184 andthe uplink receivers (URXs) 190 (which are discussed below) tosynchronize these components to the base station 69(1)-69(N). One DRX186 can be provided in the HEU 12 providing settings to the LPU 184 andall URXs 190. Alternatively, a DRX 186 can be provided for each OIC 80if desired. More detail regarding an exemplary DRX will be discussed inmore detail below with regard to FIGS. 11 and 12.

With continuing reference to FIG. 9A, the URXs 190 are provided toperform signal analysis on uplink optical RF signals 22U received fromantennas in RAUs 14 to provide the energy levels of these signals to theLPU 184 for processing. In essence, the URXs 190 listen on the uplinkoptical fiber 16U to monitor the uplink optical RF signals 22U todetermine the energy level of these signals. In this embodiment, eachURX 190 has three (3) uplink signal analyzing paths to support three (3)uplink optical RF signals 22U coming from up to three (3) RAUs 14.Implementing URX 190 functionality on the OIC 80 automatically takesinto account the scalability of the HEU 12 so that sufficient resourcesare provided to timely analyze incoming uplink optical RF signals 22U.Each analyzing path converts a specific channel that matches the channelof a base station 69(1)-69(N) to baseband and then performs spectralanalysis and energy detection for each RAU 14, respectively. The signalanalysis performed in the URXs 190 is made according to the referencetiming provided by the DRX 186. The maximum energy values of eachchannel are provided to the LPU 184 to determine the locations of clientdevices 24 and provide this information to the base stations69(1)-69(N). More detail regarding an exemplary URX will be discussed inmore detail below with regard to FIGS. 13-15.

With continuing reference to FIG. 9A, the communication link 192 may bean Ethernet communication link, which is well supported. Differentnetwork protocols, such as User Datagram Protocol (UDP) and TransmissionControl Protocol (TCP)/Internet Protocol (IP) (TCP/IP), are also wellsupported. IP packets communicated from the LPU 184 to the base stations69(1)-69(N) can also be routed via a wide area network (WAN) or via acellular modem (e.g., LTE), as examples, to remote locations. In thismanner, location processing provided by the LPU 184 can be supportedeven if the HEU 12 is remotely located from the base stations69(1)-69(N), for example, when the HEU 12 is connected to a cellularnetwork.

The base stations 69(1)-69(N) can request location processing servicesto the HEU 12 by sending a request message over the communication link192 to the HEU 12. In this instance, the LPU 184 wakes up the DRX 186and the URXs 190. Control messages from the LPU 184 to the DRX 186request the DRX 186 to tune to the same channel as the base station69(1)-69(N) requesting location services/information. The DRX 186 thenacquires the base station 69(1)-69(N) downlink signal and decodes thecontrol channel to get frame timing and cell-site specificconfiguration. These parameters are communicated from the DRX 186 to theLPU 184, which in turn configures the URXs 190 based on this parameterinformation. The URXs 190 can then monitor the uplink optical RF signals22U on the configured channel for providing energy levels of uplinkoptical RF signals 22U on the channel to the LPU 184. If a common DRX186 is provided, location services can be provided for one channelrequested by the base station 69(1)-69(N) at one time. However, ifmultiple DRXs 186 are provided in the OICs 80, location services formore than one base station channel can be performed at the same time.

FIG. 10 is a schematic diagram illustrating components that may beincluded in an LPU, which can include the LPU 184 in FIGS. 6, 9A, and9B. The LPU 184 in this embodiment includes one or more BTS ports194(1)-194(N) that allow communication between the LPU 184 and the basestations 69(1)-69(N) over the communication link 192. The BTS ports194(1)-194(N) are connected to a BTS interface 196 provided in a controlsystem 197 in the LPU 184 that is configured to receive requests todetermine locations of client devices 24 for given channels of the basestations 69(1)-69(N). The BTS interface 196 is also configured to reportto the base stations 69(1)-69(N) through the appropriate BTS port194(1)-194(N) which antenna 32 is receiving maximum energy from clientdevices 24 for determining the location of the client devices 24.

With continuing reference to FIG. 10, the LPU 184 also includes a DRXcontrol 198 that is configured to power up and reset the DRX 186 whenlocation services are requested or desired. The DRX control 198 is alsoconfigured to set the channel in the DRX 186 to distinguish downlink RFsignals from the base station 69(1)-69(N) requesting location servicesto the LPU 184. The DRX control 198 communicates to the DRX 186 in thisregard through a DRX port 200 provided in the LPU 184. Timinginformation from the DRX 186 received over a downlink RF signal from abase station 69(1)-69(N) requesting location services is provided to theLPU 184 through a timing port 202.

With continuing reference to FIG. 10, the LPU 184 also includes a URXcontrol 204 that is configured to power up and reset the URXs 190 whenlocation services are requested or desired. The URX control 204 is alsoconfigured to set the channel in the URXs 190 to distinguish uplink RFsignals from the client devices 24 destined for the base stations69(1)-69(N) requesting location services to the LPU 184. The URX control204 can also relay timing information, such as frame number and frametiming, to the URXs 190. The URX control 204 can also relay cell-sitespecific configuration data, such as cyclic prefix mode and bandwidth asexamples, to the URXs 190. The URX control 204 communicates to the URXs190 in this regard through URX ports 206(1)-206(N) provided in the LPU184.

With continuing reference to FIG. 10, the LPU 184 also includes alocation module 208 that is configured to collect data regarding energylevels of uplink RF signals from the URXs 190 over the URX ports206(1)-206(N). Thus, the LPU 184 can receive energy levels of uplink RFsignals from client devices 24 per URX 190 and per client device 24since a URX 190 is provided per OIC 80 in one embodiment. The locationmodule 208 identifies the antenna 32 (i.e., RAU 14) that has the maximumenergy signal for each client device 24. By selecting the URX 190 thathas reported the maximum energy level for a given client device 24, theclient device 24 can be associated with a specific antenna 32 in a RAU14 and thus the location of the client device 24 relative to thelocation of such antenna 32 can be determined. The location informationdetermined by the location module 208 can be provided to the basestations 69(1)-69(N) via the BTS ports 194(1)-194(N). The LPU 184includes a switch 210, which may be an Ethernet switch, thatconcentrates traffic between the components of the LPU 184 and the ports194(1)-194(N), 200, 206(1)-206(N).

The control system 197, and any of the components provided therein asillustrated in FIG. 10, may be exclusively provided in circuitry,software instructions executing on a processor, or a combination ofboth. As examples, the control system 197 may include a circuit, whichmay be provided in a field-programmable gate array (FPGA), amicroprocessor, a microcontroller, or any combination thereof. Memory207 may be provided in the control system 197 that containscomputer-executable instructions to perform some or all of thefunctionalities provided in the control system 197.

FIG. 11 is a schematic diagram of an exemplary downlink BIC 74 in FIGS.9A and 9B, which can comprise a single printed circuit board. Thedownlink BIC 74 receives the downlink electrical RF signals188(1)-188(N) from the base stations 69(1)-69(N), combines the downlinkelectrical RF signals 188(1)-188(N) via a combiner 212, and then splitsthe combined signal into twelve (12) output signals to be communicatedto the OICs 80 to be converted into downlink optical RF signals to becommunicated to RAUs 14. In this embodiment, the DRX 186 is coupled toan output 214 of the combiner 212. As an example, the expected powerlevel of the output 214 may be in the range of 8 dBm. However, as anexample, the DRX 186 may be configured to receive signal levels from theoutput 214 from −10 to −90 dBm. Thus, the DRX 186 can receive downlinkelectrical RF signals 188(1)-188(N) for all base stations 69(1)-69(N)and thus communicate requests from the base stations 69(1)-69(N)requesting location services to the LPU 184. Alternatively, multipleDRXs 186 could be provided to individually receive downlink electricalRF signals 188(1)-188(N) from the base stations 69(1)-69(N) before thedownlink electrical RF signals 188(1)-188(N) are combined. In thisinstance, each DRX would communicate to the LPU 184 to provide requestsfor location services from the base stations 69(1)-69(N).

FIG. 12 is a schematic diagram of the DRX 186 in FIGS. 9A and 9Billustrating exemplary components that can be provided in the DRX 186.In this example, the DRX 186 contains an RF transceiver 216, a clockgeneration unit 218, and a control module 220 which provides the logicfor performing time synchronization via generation of a TIMING signal219. For example, the time synchronization performed may be LTE timesynchronization. The RF transceiver 216 receives the downlink electricalRF signal 188(1)-188(N) through a BTS downlink RF signal port 217. Thecontrol module 220 may be provided exclusively in circuitry, such as inan FPGA as an example, or software executed on a processor, or acombination of both. A DRX control 222 provided in the control module220 is configured to interpret commands from the LPU 184 and send thedetected cell-site specific parameters to the LPU 184. For LTEprocessing as an example, an LTE cell searcher 224 and downlink receiver226 are included. Automatic frequency control (AFC) 228 is alsoincluded.

Using LTE processing as a specific example, the downlink receiver 226 isset up and calibrated. A control interface 230 to set up and calibratethe RF transceiver 216 is provided by a downlink receiver control 232.The LTE cell searcher 224 finds the frame timing using an LTE primarysynchronization sequence (PSS) and secondary synchronization sequence(SSS). The downlink receiver 226 is responsible for retrieving furthercontrol parameters from the broadcast channel in the downlink electricalRF signals 188(1)-188(N). Frequency synchronization can be achieved bytuning a local voltage controlled oscillator (VCO) 234. An externaldigital-to-analog converter (DAC) 236 is provided and used forgenerating the control voltage for the VCO 234. The URXs 190 aresynchronized in frequency to the uplink electrical RF signals receivedfrom the client devices 24. Thus, the VCO's 234 reference frequency isbuffered and distributed to the URXs 190 as the CLOCK signal 237 in thisembodiment. The VCO's 234 reference frequency can also be provided tothe LPU 184 for synchronization if the LPU 184 is not hosted on the samePCB as the DRX 184.

FIG. 13 is a schematic diagram of an exemplary OIC 80 provided in FIGS.9A and 9B. In this embodiment, the OIC 80 supports N number of RAUs 14on a single PCB. The OIC 80 comprises an N-way downlink splitter 238electrically coupled to a downlink coaxial connection 240, an N-wayuplink combiner 242 electrically coupled to an uplink coaxial connection244, N downlinks 246(1)-246(N), N uplinks 248(1)-248(N), N E/Oconverters 250(1)-250(N), N O/E converters 252, and connectors 254. Notethat the number of RAUs 14 supported by the OIC 80 can be varied,however, depending upon the particular application. In the illustratedembodiment, the connectors 254 are dual SC/APC interfaces. A URX 190 isprovided in the OIC 80 to tap off uplink optical RF signals256(1)-256(N) that are the output of the N-way uplink combiner 242 tofurther process such signals and provide energy levels to the LPU 184for location processing.

FIG. 14 is a schematic diagram of the URX 190 in FIGS. 9A and 9Billustrates exemplary components provided in the URX 190. In thisembodiment, the URX 190 has transceivers 258(1)-258(N), one for each OICinput 259(1)-259(N) supported by the URX 190, which down-converts anuplink electrical RF signal from a client device 24 to baseband. Acontrol module 260 is provided that contains uplink spectrum analyzers262(1)-262(N) for each OIC input 259(1)-259(N). The uplink spectrumanalyzers 262(1)-262(N) perform signal analysis on a digital basebandinput 263 to determine the energy level on the uplink electrical RFsignals on the baseband. A control interface 264 is provided in thecontrol module 260 to provide energy level information regarding uplinkelectrical RF signals received from the OIC inputs 259(1)-259(N) to theLPU 184 via an LPU port 265. The uplink spectrum analyzers 262(1)-262(N)can be configured via control signals 270(1)-270(N) provided by thecontrol interface 264 to the uplink spectrum analyzers 262(1)-262(N).The URX 190 receives the clock signal 237 from the DRX 186 through aclock port 266 to use to synchronize control logic in the control module260. For accurate timing, the uplink spectrum analyzers 262(1)-262(N)receive the timing signal 219 through a timing port 268.

FIG. 15 is a schematic diagram of an exemplary uplink spectrum analyzer262 provided in the URX 190 in FIG. 14. The uplink spectrum analyzer 262performs signal analysis on one digital baseband input 263 to determinesignal strength based on a digital representation of an uplinkelectrical RF signal. The uplink spectrum analyzer 262 in thisembodiment multiplies the digital baseband input 263 with a complexsinusoid signal using a multiplier 272, and the half sub-carrierfrequency shift of the uplink electrical RF signal is undone. In orderto determine the energy or signal strength level in the uplinkelectrical RF signal, windowing is performed by a window selector 274.On this sample vector, the FFT is computed. Then, for all usedfrequencies, the squared absolute value is computed and all squaredvalues that belong to a client device 24 are added. The results arefurther averaged over a number of symbols 276 that belong to one slot inthe example of LTE processing. The results are then serialized andprovided as output 278 to the control interface 264.

FIG. 16 illustrates exemplary URX communication messages 280(1)-280(N)communicated from the URX 190 to the LPU 184 to provide energy/signalstrength levels associated with RAUs 14 assigned to the URX 190. In thismanner, as previously described, the LPU 184 can determine for which RAUthe energy level of communications of a client device 24 is strongest.This information can indicate the location of the client device 24,since the location of the RAUs 14 in the distributed antenna system areknown. The URX communication messages 280(1)-280(N) are created by thecontrol interface 264 in the URX 190 in the example of FIG. 14 based onthe output of the uplink spectrum analyzers 262(1)-262(N).

As illustrated in FIG. 16, each URX 190 provides a URX communicationmessage 280 to the LPU 184. The URX communication message 280 isprovided over the LPU port 265 in FIG. 14 to the LPU 184 in oneembodiment. For each RAU 14 receiving communications with a clientdevice 24, a URX communication message 280 is provided to the LPU 184.The URX communication message 280 contains a URX ADDRESS 282, FRAMENUMBER 284, and SLOT # 286. In one embodiment of LTE processing, this isknown as a resource block (RB). An RB 288 contains the energy level fora client device 24 communicating with an RAU. In a LTE processingexample, RBs 288 are provided for all LTE resources blocks.

FIG. 17 is an exemplary LPU communication message 290 communicated froman LPU 184 to a base station 69(1)-69(N) to provide RAUs associated withthe maximum energy level for client device 24 communications. In thisexample, the location module 208 in the LPU 184 in FIG. 10 creates theLPU communication message 290 to send to a base station 69(1)-69(N)through BTS ports 194 over the communication link 192. The LPUcommunication message 290 provide condensed information from the URXcommunication messages 280(1)-280(N) that provide the RB 288 containingthe RAU that received the maximum energy level of communications fromclient devices 24, or RBs. Thus, when this information is provided thebase station 69(1)-69(N), the base station 69(1)-69(N) can determine towhich RAU the client devices 24 are closest, and thus the location ofthe client devices 24.

FIG. 18 is a schematic diagram of an exemplary HEU board configurationthat can be provided in the HEU 12. In this embodiment, one URX 190 isprovided per OIC 80 as illustrated in FIG. 18. This configuration hasthe advantage of modularity, but also requires more URXs 190 as OICs 80are added, thereby increasing expense and the space requirements. Thus,in this example, if the URX 190 consumes the same amount of space in theHEU 12 as the OIC 80, providing a URX 190 per OIC 80 reduces the numberof OICs 80 that can be provided in the HEU 12 by one half.

FIG. 19 is a schematic diagram of another exemplary HEU boardconfiguration. In this example, a URX 190 is provided per opticalinterface module (OIM) 300. An OIM 300 consists of two or more OICs 80.Thus, in this example, less URXs 190 are provided for a given number ofOICs 80 than the configuration in FIG. 18. This has the advantage ofsaving space when a large number of OICs 80 are included in the HEU 12.However, if a small number of OICs 80 are included in the HEU 12, theURX 190 may be more expensive since it provides resources in the URX 190to support a plurality of OICs 80 in the OIM 300 instead of just one OIC80 like provided in FIG. 18.

If it is desired to support providing location services for more clientdevices than a single HEU 12 can handle, multiple HEUs 12 can beprovided in a master/slave arrangement. In this regard, FIG. 20 is aschematic diagram of a master HEU 12(M) configured to provide locationinformation for client devices communicating with a plurality of slaveHEUs 12(1)-12(N) communicatively coupled to the master HEU 12(M). Thecomponents in the HEUs 12(M), 12(1)-12(N) have been previously describedand are not re-described here. Each slave HEU 12(1)-12(N) can providelocation information as previously described above to the master HEU12(M), and more particularly to a master LPU 184(M), which can in turnprovide such location information to the base stations 69(1)-69(N).Location services can be requested over a master communication link192(M) to the master HEU 12(M), which in turn may pass the locationservices request to the appropriate slave HEU 12(1)-12(N).

Some base stations support a transmission method using more than oneantenna to receive or transmit RF signals along different propagationpaths, for example, using antenna diversity or a multiple input/multipleoutput (MIMO) antenna scheme. In this case, more than one antenna can beused to receive the downlink signal at the head-end unit. The signalsare individually transmitted to the head-end unit and then combined withthe respective received signals. This method can provide better signalquality and increase reliability.

As previously discussed, the RF signals in the distributed antennasystems disclosed herein can be, but are not required, to be modulatedaccording to the LTE standard. LTE employs OFDM for downlink datatransmission and SC-FDMA for uplink transmission and furthermore, uses aMIMO antenna scheme for data transmission. In OFDM, a large number ofsub-carrier frequencies are used to carry the data. The sub-carriers areorthogonal to each other so that the cross-talk between the sub-channelsis eliminated. Each sub-carrier is independently modulated. Based on theorthogonality, a discrete Fourier transform (DFT) algorithm can besimply implemented on the receiver side and inverse DFT (IDFT) on thetransmitter side. Similarly in SC-FDMA, both DFT and IDFT are applied onthe transmitter side and also on the receiver side.

LTE users can be separated by the base station 69 in time and frequencydomain. A media access controller (MAC) scheduler of a base station 69is in control of assigning RBs to specific client devices 24 and hasknowledge of which RB belongs to which client device 24. For an outsideobserver, this knowledge is not readily obtainable. However, in order tolocate a client device 24 within the proximity of an RAU 14, aspreviously discussed, it can be sufficient to measure the RB energy fromthe client device 24 and send the maximum detected values together withthe RAU 14 number to the base station. The base station 69 then can takethe measurement results and relate it to the MAC scheduling information.

In this regard, FIG. 21 shows a simple example how client devices 24 areseparated by time and frequency in LTE. The base station 69 assignsdifferent RBs to different client devices 24. Due to the nature of adistributed antenna system, the base station 69 sees a superposition 310of signals 312(1)-312(N) received from the individual antennas32(1)-32(N). The base station 69 uses the scheduling information todemodulate and de-multiplex the received SC-FDMA multiplex. If the IDASreports from which antenna 32(1)-32(N) RB is received with maximumenergy, a client device 24 can be located. Thus, the location retrievalprocess can be summarized as follows for one embodiment. For eachantenna 32 and channel, detect energy for every RB. For each RB, reportmax value together with antennas 32(1)-32(N) to the base station 69. Asthe base station 69 knows each client device's 24 allocation in thesuperposition of signals, a user can be associated with an antenna.

In order to minimize interference to adjacent cells in this embodiment,LTE signals are sent typically close to the minimum required signallevel necessary to demodulate the signal at the base station. It hasbeen shown above that carrier to noise ratios can be as low as −3 dB.FIG. 22 shows the spectrum of an SC-FMDA signal that is received with aCNR of 0 dB. Also shown is the spectrum of a noise signal. It can beseen that for this level, the signal is not possible to visuallydistinguish the signal from the noise signal (i.e., the presence of theuplink signal is hard to detect). It shall also be noted that incontrast to OFDM, an SC-FDMA signal does not have a flat spectrum.

For RB energy detection, at first, the time and frequency synchronizedsignal is shifted such by one half subcarrier (i.e., 7.5 kHz to removethe one half subcarrier frequency shift that is introduced at the uplinktransmitter to avoid a possible DC notch). Then, the cyclic prefix isremoved by selecting a window of FFT SIZE samples. The FFT size varieswith the LTE channel bandwidth. On the selected samples, the FFT iscomputed and the squared absolute values of the FFT outputs arecomputed. These values are proportional to the energy received on one(1) subcarrier for one (1) SC-FDMA symbol. All squared outputs thatbelong to one (1) RB are now added to give the total RB energy. Theaddition takes place over twelve (12) adjacent FFT outputs and over six(6) or seven (7) SC-FDMA symbols depending on the LTE mode used. Thesounding reference if present needs to be omitted. As the distributedantenna system may not know when the sounding reference symbol is sent,the last SC-FDMA symbol in a subframe shall always be omitted. In orderto keep time slots symmetrical, omit the last SC-FDMA symbol in thefirst time slot of a subframe.

The robustness of the algorithm in Additive White Gaussian Noise (AWGN)channels has been analyzed. In this analysis, one client device 24 isadded to one RAU 14, the other antennas 32 are receiving white Gaussiannoise only for that RB. Each RAU 14 represents a possible communicationchannel. The client device 24 just sends one (1) RB. Detection ispositive if the received RB energy for the channel to which the clientdevice 24 is connected is highest. The results are shown in FIG. 23. Itcan be seen that if the distributed antenna system has to choose betweenmany channels (e.g., thirty-two (32)), and bases its decision solely onone RB's energy, the probability of a false decision is higher than ifthe distributed antenna system would have to choose between only two (2)channels. For low carrier-to-noise ratios of −3 dB, the probability ofmaking a wrong decision is four (4) percent in this example, whereas itwould be around 0.3 percent if the distributed antenna system would haveto decide between just two channels. For higher CNRs of like 0 dB, theprobability of a wrong decision is below 0.1 percent (i.e., the highestenergy value reported by the IDAS would point to the right RAU withlikelihood greater than 99.1 percent).

The detection probability has been further analyzed. FIGS. 24 and 25show the probability of a false detection as a function of RAU 14channels if the location information is rejected if one or more maximumresults point to different RAUs 14, in this example. This is done for 10or 100 RBs, respectively. As more observations are made, the probabilityfor rejected location information increases with the number ofobservations.

For a CNR of −3 dB and thirty-two (32) RAU 14 channels, the probabilityof having at least one RB pointing at the wrong channel using themaximum energy criterion is close to 100 percent. An alternative for abase station 69 is to choose the most likely antenna after multipleobservations (i.e., select the RAU 14 that is most often reported). FIG.25 also shows the probability that more than 50 out of 100 observationspoint to the correct RAU 14 for thirty-two (32) RAU 14 channels. Thiscurve can be seen as an upper bound for making a wrong decision. Usingthis method, it can be seen from FIG. 25 that an LTE user can be locatedwith a probability of greater than 99.9 percent even if the received CNRis as low as −5 dB and fulfills all requirements on location processingwith margin.

The impact of frequency offset has been analyzed. Frequency offsetdestroys the orthogonality of the SC-FDMA signal. In this regard, FIG.26 shows the energy leakage that is caused by frequency offset. It canbe seen that one percent of the subcarrier spacing causes −37 dBleakages (i.e., an adjacent signal on a different RAU that is receivedat the base station 37 dB stronger than the signal for which thelocation needs to be determined can cause a wrong decision). One percentsubcarrier spacing corresponds to 150 Hz. For three percent, i.e., 450Hertz (Hz), the leakage already increases to −28 dB. It shall be notedthat at a signal frequency of 2 GigaHertz (GHz), 150 Hz frequency offsetcan be caused by an oscillator inaccuracy of, i.e., 75 parts per billionwhich is a factor 500 less than the accuracy of an off-the-shelvecrystal oscillator. Thus, frequency synchronization is performed. Thefrequency can be synchronized to the base station's downlink signalthrough standard techniques that are also used in mobile terminals.

Like frequency offset, time offset destroys the orthogonality of theSC-FDMA signal. FIG. 27 shows the energy leakage as a function of timeoffset relative to the length of the cyclic prefix. A time offset causesintersymbol interference. At a time offset of twenty (20) percent of thecyclic prefix (approximately 1 pec), the leakage already has reached −15dB. This would mean that a terminal that is received at the base station15 dB stronger than the terminal whose location needs to be determinedcan significantly impact the location detection capabilities of thesystem. Therefore, time synchronization is performed. The symbol timingcan be synchronized to the base station's downlink signal throughstandard techniques that are also used in mobile terminals. The accuratetime shall be distributed over a dedicated wire.

Further, as used herein, it is intended that terms “fiber optic cables”and/or “optical fibers” include all types of single mode and multi-modelight waveguides, including one or more optical fibers that may beupcoated, colored, buffered, ribbonized and/or have other organizing orprotective structure in a cable such as one or more tubes, strengthmembers, jackets or the like. Likewise, other types of suitable opticalfibers include bend-insensitive optical fibers, or any other expedientof a medium for transmitting light signals. An example of abend-insensitive, or bend resistant, optical fiber is ClearCurve®Multimode fiber commercially available from Corning Incorporated.Suitable fibers of this type are disclosed, for example, in U.S. PatentApplication Publication Nos. 2008/0166094 and 2009/0169163.

Those of skill in the art would further appreciate that the variousillustrative logical blocks, modules, circuits, and algorithms describedin connection with the embodiments disclosed herein may be implementedas electronic hardware, instructions stored in memory or in anothercomputer-readable medium and executed by a processor or other processingdevice, or combinations of both. The memory controllers, arbiter, masterunits, and sub-master units described herein may be employed in anycircuit, hardware component, IC, or IC chip, as examples. The memory maybe any type and size of memory and may be configured to store any typeof information desired. To clearly illustrate this interchangeability,various illustrative components, blocks, modules, circuits, and stepshave been described above generally in terms of their functionality. Howsuch functionality is implemented depends upon the particularapplication, design choices, and/or design constraints imposed on theoverall system. Skilled artisans may implement the describedfunctionality in varying ways for each particular application, but suchimplementation decisions should not be interpreted as causing adeparture from the scope of the present invention.

The various illustrative logical blocks, modules, and circuits describedin connection with the embodiments disclosed herein may be implementedor performed with a processor, a Digital Signal Processor (DSP), anApplication Specific Integrated Circuit (ASIC), a Field ProgrammableGate Array (FPGA) or other programmable logic device, discrete gate ortransistor logic, discrete hardware components, or any combinationthereof designed to perform the functions described herein. A processormay be a microprocessor, but in the alternative, the processor may beany conventional processor, controller, microcontroller, or statemachine. A processor may also be implemented as a combination ofcomputing devices, e.g., a combination of a DSP and a microprocessor, aplurality of microprocessors, one or more microprocessors in conjunctionwith a DSP core, or any other such configuration.

The embodiments disclosed herein may be embodied in hardware and ininstructions that are stored in hardware, and may reside, for example,in Random Access Memory (RAM), flash memory, Read Only Memory (ROM),Electrically Programmable ROM (EPROM), Electrically ErasableProgrammable ROM (EEPROM), registers, hard disk, a removable disk, aCD-ROM, or any other form of computer readable medium known in the art.An exemplary storage medium is coupled to the processor such that theprocessor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor. The processor and the storage medium may reside in anASIC. The ASIC may reside in a remote station. In the alternative, theprocessor and the storage medium may reside as discrete components in aremote station, base station, or server.

Many modifications and other embodiments of the embodiments set forthherein will come to mind to one skilled in the art to which theembodiments pertain having the benefit of the teachings presented in theforegoing descriptions and the associated drawings. These modificationsinclude, but are not limited to, whether a tracking signal is provided,whether downlink and/or uplink BICs are included, whether trackingsignal inputs are provided in the same distributed communications unitas downlink base station inputs, the number and type of OICs and RAUsprovided in the distributed antenna system, etc.. Therefore, it is to beunderstood that the description and claims are not to be limited to thespecific embodiments disclosed and that modifications and otherembodiments are intended to be included within the scope of the appendedclaims. It is intended that the embodiments cover the modifications andvariations of the embodiments provided they come within the scope of theappended claims and their equivalents. Although specific terms areemployed herein, they are used in a generic and descriptive sense onlyand not for purposes of limitation.

What is claimed is:
 1. A wireless communication system wirelessconfigured to receive and distribute downlink radio frequency (RF)signals and receive and distribute uplink RF signals, comprising: aplurality of fiber optic cables; a plurality of remote units, eachremote unit being optically coupled to at least one of the fiber opticcables, and each remote unit comprising at least two antennas in adiversity arrangement, the plurality of remote units configured to use amultiple input/multiple output (MIMO) scheme and installed in knownlocations, the plurality of remote units configured to: receive thedownlink RF signals as optical downlink RF signals; convert the opticaldownlink RF signals into electrical downlink signals; transmit thedownlink RF signals into a respective coverage area; receive uplink RFsignals from client devices located in respective coverage areas; anddistribute the received uplink RF signals; and a location processingunit (LPU), comprising: a plurality of signal monitoring devicesconfigured to receive each of the uplink RF signals distributed from theplurality of remote units located in the known locations; and acontroller configured to: determine signal strengths of the receiveduplink RF signals; determine which remote unit among the plurality ofremote units is receiving the uplink RF signals from at least one clientdevice having the greater signal strength; and determine locationinformation for the at least one client device based on identificationof the remote unit receiving the uplink RF signals having the greatersignal strength.
 2. The wireless communication system of claim 1,wherein the received uplink RF signals are received in channelsseparated into frequency blocks.
 3. The wireless communication system ofclaim 2, wherein the controller is configured to determine the signalstrength of the uplink RF signals by measuring the signal strength ofthe frequency blocks in the uplink RF signals.
 4. The wirelesscommunication system of claim 2, wherein the controller is furtherconfigured to convert the received uplink RF signals into basebanduplink RF signals, and wherein the controller is further configured tosynchronize to a downlink RF signal received from a base station.
 5. Thewireless communication system of claim 2, wherein the received uplink RFsignals are received into resource blocks (RB) separately identifiableto a particular user device.
 6. The wireless communication system ofclaim 1, wherein the received uplink RF signals are received in channelsseparated into temporal blocks.
 7. The wireless communication system ofclaim 6, wherein the controller is configured to determine the signalstrength of the uplink RF signals by measuring the signal strength ofthe temporal blocks in the uplink RF signals.
 8. The wirelesscommunication system of claim 6, wherein the controller is configured todetermine the signal strengths of the uplink RF signals as a function ofa fast Fourier transform (FFT) of a window of samples of the uplink RFsignals.
 9. A wireless communication system configured to receive anddistribute downlink radio frequency (RF) signals and receive anddistribute uplink RF signals, comprising: at least one optical fibercable; the plurality of remote units, each remote unit being opticallycoupled to the at least one optical fiber cable, and each remote unitcomprising: at least two antennas in a diversity arrangement, theplurality of remote units configured to use a multiple input/multipleoutput (MIMO) scheme and installed in known locations; at least oneoptical-to-electrical (0/E) converter; and at least oneelectrical-to-optical (E/O) converter, the a plurality of remote unitsconfigured to: receive the downlink RF signals as optical downlink RFsignals; convert the optical downlink RF signals into electricaldownlink signals at the at least one O/E converter; transmit thedownlink RF signals into a respective coverage area; receive uplink RFsignals from client devices located in respective coverage areas; anddistribute the received uplink RF signals; and a location processingunit (LPU), comprising: a plurality of signal monitoring devicesconfigured to receive each of the uplink RF signals distributed from theplurality of remote units located in the known locations; and acontroller configured to: determine signal strengths of the receiveduplink RF signals; determine which remote unit among the plurality ofremote units is receiving the uplink RF signals from at least one clientdevice having the greater signal strength; and determine locationinformation for the at least one client device based on identificationof the remote unit receiving the uplink RF signals having the greatersignal strength.
 10. The wireless communication system of claim 9,wherein the received uplink RF signals are received in channelsseparated into frequency blocks.
 11. The wireless communication systemof claim 10, wherein the controller is configured to determine thesignal strength of the uplink RF signals by measuring the signalstrength of the frequency blocks in the uplink RF signals.
 12. Thewireless communication system of claim 10, wherein the controller isfurther configured to convert the received uplink RF signals intobaseband uplink RF signals.
 13. The wireless communication system ofclaim 9, wherein the received uplink RF signals are received in channelsseparated into temporal blocks.
 14. The wireless communication system ofclaim 13, wherein the controller is configured to determine the signalstrength of the uplink RF signals by measuring the signal strength ofthe temporal blocks in the uplink RF signals.
 15. A wirelesscommunication system deployed in a building infrastructure andconfigured to receive and distribute downlink radio frequency (RF)signals and receive and distribute uplink RF signals, comprising: aplurality of optical fiber cables; the plurality of remote unitsoptically coupled to the optical fiber cables and distributed overmultiple floors of the building infrastructure, and each remote unitcomprising at least two antennas in a diversity arrangement, theplurality of remote units configured to use a multiple input/multipleoutput (MIMO) scheme and installed in known locations, the a pluralityof remote units configured to: receive the downlink RF signals asoptical downlink RF signals; convert the optical downlink RF signalsinto electrical downlink signals; transmit the downlink RF signals intoa respective coverage area; receive uplink RF signals from clientdevices located in respective coverage areas; and distribute thereceived uplink RF signals; and a location processing unit (LPU),comprising: a plurality of signal monitoring devices configured toreceive each of the uplink RF signals distributed from the plurality ofremote units located in the known locations; and a controller configuredto: determine signal strengths of the received uplink RF signals;determine which remote unit among the plurality of remote units isreceiving the uplink RF signals from at least one client device havingthe greater signal strength; and determine location information for theat least one client device based on identification of the remote unitreceiving the uplink RF signals having the greater signal strength. 16.The wireless communication system of claim 15, wherein the receiveduplink RF signals are received in channels separated into frequencyblocks.
 17. The wireless communication system of claim 16, wherein thecontroller is configured to determine the signal strength of the uplinkRF signals by measuring the signal strength of the frequency blocks inthe uplink RF signals.
 18. The wireless communication system of claim15, wherein the received uplink RF signals are received in channelsseparated into temporal blocks.
 19. The wireless communication system ofclaim 18, wherein the controller is configured to determine the signalstrength of the uplink RF signals by measuring the signal strength ofthe temporal blocks in the uplink RF signals.